1. Field of the Invention
The present invention relates to a scroll compressor which is, for example, used for a refrigerant compressor in refrigerating system.
2. Background of the Invention
Scroll compressors are well known and include, as in, for example, Japanese Un-Examined Patent Publication No. 60-85285, a housing, a stationary scroll member fixedly arranged in the housing, the stationary scroll member having a base plate and a scroll wall extending from the base plate, and a movable scroll member rotatably arranged in the housing at a phase difference of 180 degrees with respect to the stationary scroll member, the movable scroll member having a base plate and a scroll wall extending from the base plate. Furthermore, a drive shaft is rotatably supported with respect to the housing by way of a bearing unit. A drive key is connected at an end of the shaft adjacent the movable scroll member having a boss portion extending from the base plate of the movable scroll member at its side remote from the scroll wall. The drive key is connected to the boss portion of the movable scroll member via a bushing and a radial bearing. A mechanism is arranged between the housing and the base plate of the movable scroll member for preventing the movable scroll member from rotating about its own axis.
In this compressor, the rotating movement of the pin caused by a rotating movement applied to the drive shaft is transmitted to the movable scroll member via the bushing. The self rotation blockage mechanism prevents the movable scroll member from rotating about its own axis. As a result, only an orbital movement of the movable scroll member about the axis of the shaft is obtained. Due to the orbital movement of the movable scroll member, compression chambers formed between the stationary and movable scroll members, which are in mutual engagement, are moved radially inwardly, while their volume is reduced, so that a gaseous refrigerant sucked into the chambers from an intake port is first, compressed and, second, discharged through an outlet port.
In the operation of the scroll compressor, a cantilever arrangement of the movable scroll member eccentric to the drive shaft generates a force which urges the movable scroll member to be skewed with respect to the stationary scroll member about the center of gravity of the movable scroll member due to the fact that the movable scroll member is subjected to a centrifugal force by the orbital movement as well as a compression reaction force by the refrigerant gas being compressed in the chamber. Due to an assembly tolerance for allowing the movable scroll member to be assembled to the stationary scroll member, an axial gap between the stationary and movable scroll members, and a radial gap due to the radial bearing between the movable scroll member and the drive pin, are inevitably created. The existence of such gaps allows the movable scroll member to be slightly inclined with respect to the axis of the shaft when the above mentioned skewing force is generated, thus causing the movable and stationary scroll members to be locally contacted with each other, thereby causing galling or seizing within the pump.
In a type of the scroll compressor where the stationary scroll member is fixedly arranged inside the housing, the skewed movement of the movable scroll member is likely to cause locally increased contacting pressures. Such increased contacting pressures can occur especially at locations between an outer edge at a section of the base plate of the movable scroll member without a scroll wall and an inner edge of the scroll wall of the stationary scroll member at a section where the scroll wall is connected to the housing. Namely, at these locations, a relative lateral movement between the inner and outer scrolls occurs. The skewed arrangement of the movable scroll member with respect to the stationary scroll member subjects the inner and outer edges to an increased contact force, thereby causing galling or seizing. In this situation, prolonged operation of the compressor under a high compression may damage the movable scroll member or the housing or the stationary scroll member connected to the housing.
In this type of scroll compressor, the Japanese Examined Patent Publication No. 63-32992 or Unexamined Patent Publication Number 2-146201 proposes a construction for obtaining both low weight and low friction wherein one of the stationary scroll member and the movable scroll member is made of a soft material such as an aluminum based alloy, while the other one is made of a hardened material such an aluminum based alloy with alumite treatment. In such a construction of a scroll compressor, skewed movement of the movable scroll member with respect to the stationary scroll member may make it more easy to generate galling and seizing.